1. Technical Field
The present invention relates to the field of inks, and in particular, to a stable color-changing ink.
2. Related Art
With the continuous development of the microcapsule pigment synthesis technology in China, the color changing form of microcapsule pigments shows a trend of diversification, and microcapsule pigments are mainly used in the industries of plastics, textiles, printing, coatings and inks. By adding a microcapsule color-changing pigment, the application functions of the product is increased, and the added value of the product is improved, thereby making the various industries have more vigor. However, few people use microcapsule pigments in stationery writing tools, because the ink quality requirements for writing tools are very high. Furthermore, the particle diameter of the microcapsule pigment is large (generally 1 to 20 μm), and the average particles diameter can merely be controlled within the range of 1 to 3 micrometers, which far exceeds the nanoscale diameter of common inks, and therefore, the stability of the ink system becomes a problem. At the same time, due to large particle diameter, the stability of the writing effect is influenced, and hollow phenomenon, ink accumulation phenomenon, disconnection phenomenon and other phenomena occur.
In the writing ink industry standards, the stability of common inks needs to be detected by a high-temperature baking detection, high-speed centrifugation detection and scribing length detection. As for the hardest high-speed centrifugation detection, the ink is generally centrifuged by a high-speed centrifuge for 1 to 2 hrs at a speed of 2000 rpm or 2500 rpm, and the stability is determined according to the difference in color between the upper layer and the lower layer of the centrifuged ink, and color consistency of the upper layer and the lower layer indicates that the stability is high.
Presently, Chinese Patent Application Publication No. CN 102575123 A, of which the Publication Date is Jul. 11, 2012 and the applicant is PILOT INK CO., LTD, discloses a reversibly thermochromic water-based ink composition, which includes water, a water soluble organic solvent, a reversibly thermochromic microcapsule pigment, a comb-like polymer dispersant having a carboxyl group on the side chain, an organic compound containing nitrogen and sulfur and a water soluble resin. The reversibly thermochromic microcapsule pigment contains: (A) an electron-donating color-rendering organic compound, (B) electron-accepting compound, and (C) a reversibly thermochromic composition formed by a reaction medium that determines the reaction temperature of the chromogenic reaction of (A) and (B) The friction color-changing gel pen formulated according to this formula cannot meet the standard in the high-speed centrifugation detection, after the high-speed centrifuge rotates for 30 min at a speed of 2000 rpm, pen point blockage and ink layering occur, so that the application and promotion of this formula or the microcapsule color-changing pigment are limited, for example, this formula or the microcapsule color-changing pigment cannot be used in push-type or direct-fluid watercolor pens, writing brushes, pens, inkjet inks. Possible reasons lie in that, in addition to controlling the particle diameter of the microcapsule color-changing pigment, some other disadvantages or some places needing to be improved still exist. In this formula, the average particle diameter (the average value of the maximum diameter) of the microcapsule pigment is within the range of 0.5 to 5.0 μm, preferably within the range of 1.0 to 4.0 μm, and more preferably within the range of 1.0 to 3.0 μm.